Insulating glass units (IGUs) are formed by mating at least two panes of glass to a stand-off system so that at least one cavity is formed between the panes, thereby improving the insulating level relative to a single-pane unit. Vacuum insulated glass units (VIGUs) are a special type of IGU where the cavity/cavities between the panes is evacuated, preferably below a pressure of 1 mtorr (i.e., 1 mtorr=1×10−3 torr).
IGUs of all types use one or more seals to reduce permeability. For insulating glass units (IGUs) that use an internal or external spacer or frame to create the internal cavity, the seals reduce the rate of loss of the fill-gas for gas-filled IGUs and reduce the rate of ingress of ambient air and moisture into the IGU's cavity. For VIGUs, some current sealing technologies use brittle ceramic bonds such as glass frits. These are costly, require high temperature application, and are prone to reliability failures. By contrast, adhesives allow for low-temperature bonding with very high glass-to-metal bond strength, and are extremely inexpensive and also highly reliable. However, the permeability of conventional adhesives is several orders of magnitude too high to maintain the high vacuum requirements of VIGUs. A need exists therefore exists, for a multi-pane glass unit with reliable seals of reduced permeability.
VIGUs are further challenged in that some glazing materials that are conventionally seen as hermetic, for example, some compositions of silica glass, are still sufficiently permeable to gases such as helium that the VIGU's internal cavity pressure can rise above 1×10−3 torr over the desired service life of the unit. Other materials, such as metals, can outgas hydrogen at a significant rate, and thereby degrade the quality of the vacuum in the VIGU over its desired service life. A need therefore exists, for a VIGU comprising materials having improved hermeticity, so as to better meet the specifications of the window industry.